The invention relates generally to ion implanters for the manufacture of semiconductor wafers, and more particularly to a mechanism for tilting and twisting wafer support pedestals in batch-type ion implanters.
Ion implanters are used to introduce conductivity-altering impurities into semiconductor wafers. In order to accomplish this, the desired impurity material is ionized via an ion source, and then accelerated to form an ion beam of prescribed energy. The ion beam is then directed at the surface of the semiconductor wafer so that the ions in the beam penetrate the semiconductor material and are embedded in the crystalline lattice thereby forming a region of desired conductivity.
In semiconductor wafer manufacturing, there are several important considerations in achieving an effective ion implanter. One important factor is throughput, or the number of wafers processed per time unit. In addition, wafer transfer time, ion implant time and down time are other important considerations. Another important factor is the ability to implant at high angle tilt. A high tilt angle, generally in the range of about 20 to about 35 degrees, allows doping of the silicon structure beneath an obstruction to the beam. Because some electronic devices are oriented in an orthogonal relationship with respect to each other on a wafer, high tilt doping must be performed in each of four quadrants. Thus it is further desirable to be able to rotate or twist the wafer about a longitudinal axis passing through its center.
Commercial ion implanters generally comprise two different types of machines: serial and batch. In serial systems, wafers are processed one at a time. Typical batch ion implanters utilize a rotating disk, upon which wafers to be processed are mounted on pedestals located about the periphery of the disk. While modern serial implant systems provide for high tilt angle implantation and wafer rotation, serial systems that employ beam scanning have a major disadvantage of dose uniformity as compared to batch systems that employ mechanical scanning systems. In addition, because batch systems implant an entire batch of wafers in a single implant process, the heat generated by the ion beam is distributed among the wafers in the batch, making wafer cooling easier to manage. While batch systems have the advantage of high throughput of wafers, one major disadvantage of prior art batch systems is that they do not provide for high tilt angle implantation, nor do they provide for wafer rotation while the wafer remains on the disk. Furthermore, the centrifugal load caused by the wafers positioned about the periphery of the spinning disk greatly increases the mechanical complexity of the system.
Thus, a batch implant system capable of high wafer throughput, uniform dose, and provided with the capability of high tilt angle implantation and wafer rotation is desired.
The invention provides in one aspect a wafer pad assembly disposed within an ion implanter, and upon which a wafer may be mounted and rotated or indexed. The wafer pad assembly includes a wafer support pad having an upper surface for mounting the wafer and a lower surface. The lower surface is rotationally mounted to a frame of the wafer pad assembly. The lower surface of the wafer support pad further comprises a flange rotationally connected to a shaft; the shaft being connected to an actuator for selectively indexing the shaft wherein the wafer support pad is rotationally indexed.
The invention provides in another aspect a wafer pad assembly disposed within an ion implanter, and upon which a wafer may be mounted and tilted. The wafer pad assembly includes a wafer support pad having an upper surface for mounting the wafer and a lower surface, the lower surface being fixedly connected to an inner surface of a curved frame. The curved frame further comprises an outer curved surface being rotatably mounted within a corresponding mating bearing surface of a housing. The curved frame is connected to a plurality of linkages for rotating the wafer support pad within the curved frame.
These and other aspects and advantages of the present invention will be readily understood and appreciated by those skilled in the art from the following detailed description of the preferred embodiments with the best mode contemplated for practicing the invention in view of the accompanying drawings.